Reaction of titanium and zirconium particles in cylindrical explosive charges

The critical conditions for the reaction of particles of the transition metals titanium (Ti) and zirconium (Zr) dispersed during the detonation of long cylindrical explosive charges have been investigated experimentally. The charges consisted of packed beds of either spherical Ti particles or irregularly shaped Zr particles saturated with sensitized liquid nitromethane. For the Ti particles, a threshold particle diameter exists of 65 +/- 25 mu m, above which self-sustained particle reaction is not observed for charge diameters up to 49 mm, although some particle reaction occurs immediately behind the detonation front then rapidly quenches. For the smallest particles (40 mu m), the proportion of the conical particle cloud that reacts increases with charge diameter, suggesting that the reaction is a competition between particle heating and expansion cooling of the products. For 375 and 550 pm Zr particles, particle ignition was observed for 19 and 41 mm dia charges. In this case, interaction of the detonation wave with the particles is sufficient to initiate reaction at the particle surface after a delay time (similar to 5 mu s), which is much less than the time required for thermal equilibration of the particles.